In recent years, it has become almost common to transmit not only speech data but also large volume data such as still image data and moving image data, along with the increasing adoption of multimedia-enabled information in cellular mobile communication systems. Meanwhile, studies have been actively carried out to achieve a higher transmission-rate using a wide radio band, multiple-input multiple-output (MIMO) transmission technology, and interference control technique in long-term evolution advanced (LTE-Advanced).
In addition, studies have been carried out to achieve a higher transmission rate at hotspots through the deployment of small cells, each being a base station using low transmission power (may be referred to as “eNB”) in a cellular mobile communication system in LTE-Advanced. In addition, allocating a frequency different from that for macro cells as a carrier frequency for operating small cells has been under study (see Non-Patent Literature (hereinafter, abbreviated as “NPL”) 1).
In addition, operating small cells by using a carrier configuration called “New Carrier Type (NCT),” which is different from the carrier configuration used until LTE-Advanced Rel. 11 (i.e., Backward Compatible Carrier (BCT), see FIG. 1A, for example), has been under discussion. In NCT, studies have been carried out on reducing a physical downlink control channel (PDCCH) and a cell specific reference signal (CRS) transmitted in BCT and using an enhanced PDCCH (EPDCCH) for transmission of a downlink (DL) control signal and using a demodulation reference signal (DMRS) for demodulation of a signal (see, FIG. 1B, for example). An EPDCCH is mapped in a data region, and the base station is capable of specifying a frequency resource and then transmitting the EPDCCH. Accordingly, the transmission using an EPDCCH enables controlling transmission power for a control signal, or controlling interference given to a different cell by the control signal to be transmitted, or controlling interference given to a cell of the base station from a different cell.
In addition, studies have been carried out on a situation where terminals (UE: User Equipment) are connected to both a macro cell and small cell and also on a situation where UEs are connected to only a small cell. The carrier to be used in a small cell in the situation where terminals (UE: User Equipment) are connected to both a macro cell and small cell is called “Non-standalone-NCT (NS-NCT).” Meanwhile, the carrier to be used in a small cell in the situation where UEs are connected to only a small cell is called “standalone-NCT (S-NCT).”
When a UE connects to a small cell using NS-NCT, it is likely that the UE connects to a macro cell first and is then instructed by the macro cell to connect to the small cell using NS-NCT. Thus, small cells using NS-NCT can perform processing to connect UEs with support from a macro cell.
Meanwhile, since small cells using S-NCT receive no support from a macro cell, the small cells themselves need to allow UEs to connect to the small cells. In addition, the small cells using S-NCT are expected to support not only connective mode UEs, but also idle mode UEs performing no data communication. The possibility of implementing this configuration has been under discussion as well. To put it differently, the small cells each using S-NCT need to be configured to transmit information to idle mode UEs in order for the idle mode UEs to recognize the presence of small cell (e.g., cell detection), when S-NCT is used.
In BCT in which a macro cell is put into operation, each idle mode UE performs synchronization and cell detection using a primary synchronization signal (PSS)/secondary synchronization signal (SSS). After acquisition of the cell ID of a macro cell, the idle mode UE receives a master information block (MIB) and thereby acquires a transmission band, physical HARQ indicator channel (PHICH) mapping information, and a frame number and/or the like. Thereafter, the UE monitors a common search space (CSS) on a PDCCH configured with a shift pattern defined the cell ID, and blindly detects downlink control information pieces (DCIs) on the system information, paging, and a random access channel (RACH). The DCIs on the system information, paging, and RACH are masked with SI-RNTI, P-RNTI, and RA-RNTI or the like, respectively. Note that, the eNB does not recognize that idle mode UEs monitor the cell provided by the eNB, so that the eNB cannot transmit information to the idle mode UEs, using a UE-specific control signal.